Coincident with the 2010 Deepwater Horizon oil spill, unprecedented numbers of Kemp’s ridley sea turtles (Lepidochelys kempii) stranded on northern Gulf of Mexico beaches and the number of nests recorded on the primary nesting beaches plummeted far below expected levels. High levels of strandings have continued since 2010 and the number of nests recovered to approximately 2009 levels in 2011, and improved slightly in 2012. A stock assessment conducted in 2012 indicated that a mortality event occurred in 2010, and that the number of nests should once more exhibit an increasing trend from 2013 and beyond. This has not happened; rather, the number of nests declined sharply in 2013. We conducted a new stock assessment to evaluate additional scenarios, including 1) three stock-recruitment options; 2) the potential that a new source of ongoing mortality is present; and 3) the potential that the number of nests- per-adult-female is dependent on the size of the age-2þ benthic population. The latter model provided the best fit to the data. Further, the preliminary estimate of actual nesting in 2014 is consistent with model projections. The reduction in reproductive output could be due to the combination of a large population and reduced prey levels. Together these may have increased the remigration interval or reduced the number of nests per female. However, research is needed to evaluate this and other plausible hypotheses. Nesting may be highly variable in the future depending on feeding conditions on the foraging grounds.
The history of the critically endangered Kemp’s ridley sea turtle (Lepidochelys kempii) has presented scientists and conservationists with a variety of questions and challenges originating in part from the species’ limited distribution and single primary nesting beach. Although the species was initially brought to the attention of the scientific community in 1880 by Richard Kemp, more than 80 yr passed before Henry Hildebrand revealed the location of its primary nesting beach at Rancho Nuevo, Mexico in the western Gulf of Mexico. By the time scientists began estimating the number of females nesting at Rancho Nuevo, it appeared that the species had declined when compared with the relatively large mass nesting (a.k.a. arribada) filmed by Andres Herrera in 1947. This decline appeared to be due to historic exploitation of turtles and their eggs on the nesting beach and accidental capture in the Gulf of Mexico shrimp fishery. Despite the implementation of conservation measures at Rancho Nuevo, the species continued to decline until the mid-1980s. The continued protection of females and nests on the nesting beach, the decline in shrimping effort in the Gulf of Mexico, and the implementation of turtle excluder devices resulted in a significant increase in the number of females nesting during the 1990s, and an exponential recovery rate. Since 2010, the recovery rate has unexpectedly deviated from its exponential trend and sharp declines have been documented in some years. The underlying cause(s) of the recent decline is unclear.